The outer surface of a boat hull needs to resist fouling. Fouling has conventionally been inhibited by antifouling paints containing a biocide for marine organisms, which biocide is gradually leached from the paint. More recently, antifouling paints based on a hydrolysable copolymer, such as a triorganotin copolymer, have been used; in these paints the paint film is gradually dissolved from the surface of the hull as the boat moves through the sea water. However, there has recently been concern about the environmental effect of biocides released by leaching or hydrolysis from such paints, particularly from yachts and pleasure boats which are moored near the shore. There have been proposals for non-biocidal antifouling materials which do not release a poison for marine organisms but which resist the adhesions of marine fouling organisms. For example British Patents 1307001, 1470465 and 1581727, U.S. Pat. No. 3702778 and European Patents 16195 and 32597 and UK Patent Application 2141436 suggest the use of a silicone rubber, especially a room-temperature-vulcanised silicone rubber, on marine surfaces to prevent fouling. There are, however, difficulties in applying a room-temperature-vulcanisable silicone rubber to a boat hull because the silicone rubber has very low adhesion to materials used for boat construction. Such silicone rubber antifoulings have been used to a small extent on static marine structures but have not been used commercially on ships' hulls. French Patent 2157074 suggests the use of fluorinated resins as non-biocidal antifoulings.
Many boat hulls are made by applying layers of a curable resin, particularly a fibre-reinforced resin, to a mould and curing the resin the mould. The mould is usually a female mould, that is to say the layers of resin are applied inside the mould so that the layer first applied to the mould becomes the outermost layer of the boat hull. The boat hull may be made in one piece or in parts, particularly halves, which are then secured together. The mould is itself generally formed from glass-fibre-reinforced polyester resin. In an alternative procedure the boat hull or part thereof can be made by applying layers of resin to a former or male mould and curing them in the mould so that the last applied layer forms the outermost layer of the boat hull.
Swedish Patent Application 8001826 relates to a moulding technique for boat hulls in which the mould release agent, which contains an antifouling agent and may be a mixture of a fluorocarbon polymer and an antifouling agent, is transferred to the moulded boat hull. British Patents 1600120 and 2084488 and European Patent 46354 describe applying a mixture of copper particles and a suitable resin to the mould face when moulding a boat hull or other underwater structure.
U.S. Defensive patent publication No. 686959 describes a technique of viscous drag reduction of aircraft by forming fine grooves or "riblets" parallel to the airflow over the aircraft surface. It suggests that the technique can be applied to a boat hull.